Load control device for controlling a driver for a lighting load

ABSTRACT

A load control device is configured to generate a control signal having a desired magnitude for controlling a load regulation device adapted to control the power delivered to an electrical load. The load control device may comprise a control terminal arranged to provide the control signal to the load regulation device, a communication circuit for generating the control signal, and a control circuit configured to generate an output signal that is provided to the communication circuit. The communication circuit may be characterized by non-linear operation. The control circuit may adjust the magnitude of the output signal in response to the difference between the magnitude of the control signal and the desired magnitude to adjust the magnitude of the control signal towards the desired magnitude. The control circuit may also be configured to determine if an incompatible load regulation device is coupled to the load control device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.17/087,091 filed Nov. 2, 2020; which is a continuation of U.S. patentapplication Ser. No. 16/596,106, filed Oct. 8, 2019 (now U.S. Pat. No.10,826,407), which is a continuation of U.S. patent application Ser. No.16/118,406, filed Aug. 30, 2018 (now U.S. Pat. No. 10,461,661), which isa divisional of U.S. patent application Ser. No. 14/813,006, filed Jul.29, 2015 (now U.S. Pat. No. 10,236,789), which claims the benefit ofU.S. Provisional Application No. 62/059,180, filed Oct. 3, 2014, andU.S. Provisional Application No. 62/032,183, filed Aug. 1, 2014, thedisclosures of which are incorporated by reference herein in theirentireties.

BACKGROUND

A lighting source, such as light emitting diode (LED) light source, istypically driven by a load regulation device (e.g., such as an LEDdriver) in order to illuminate. A common control method for dimming anLED driver is “zero-to-ten-volt” (0-10V) control, which is sometimesreferred to as 1-10V control. A 0-10V LED driver receives power from anAC power source, with an external mechanical switch typically coupledbetween the AC power source and the 0-10V driver to provide switched-hotvoltage to the driver. The 0-10V driver controls the intensity of theconnected LED light source in response to a 0-10V control signalreceived from an external 0-10V control device. Often, the 0-10V controldevice is mounted in an electrical wallbox and comprises an intensityadjustment actuator, e.g., a slider control. The 0-10 V control deviceregulates the direct-current (DC) voltage level of the 0-10 V controlsignal provided to the driver between a substantially low voltage (i.e.,zero to one volt) to a maximum voltage (i.e., approximately ten volts)in response to an actuation of the intensity adjustment actuator.

An external 0-10V control device may include a current sink circuitand/or a current source circuit that operates in a non-linear manner.Due to the non-linear operation of the current sink/source circuitand/or the hardware of the driver, the actual magnitude of a 0-10Vcontrol signal provided by the current sink/source circuit may notcorrespond with a desired intensity level, as determined by a controllerof the 0-10V control device and provided to the current sink circuit.Accordingly, there is a need for a control device that can compensatefor the error introduced by the current sink circuit of the controldevice and/or the hardware of the driver.

SUMMARY

As described herein, a load control device may be configured to generatea control signal having a desired magnitude for controlling a loadregulation device adapted to control the power delivered from an ACpower source to an electrical load. The electrical load may be, forexample, a light emitting diode (LED) light source. The load controldevice may comprise a control terminal adapted to be coupled to the loadregulation device for providing the control signal to the loadregulation device, a communication circuit coupled to the controlterminal for generating the control signal, and a control circuitconfigured to generate an output signal that is provided to thecommunication circuit. The communication circuit may be characterized bynon-linear operation. The communication circuit may be, for example, a0-10V communication circuit for generating a 0-10V control signal. Thecontrol circuit may be configured to adjust the magnitude of the outputsignal to cause the communication circuit to adjust the magnitude of thecontrol signal to a desired magnitude, where the desired magnitudeindicates a target amount of power to be delivered to the electricalload. The control circuit may be configured to receive a feedback signalindicating the magnitude of the control signal. The control circuit maybe further configured to determine a difference between the magnitude ofthe control signal and the desired magnitude and to adjust the magnitudeof the output signal in response to the difference between the magnitudeof the control signal and the desired magnitude, so as to adjust themagnitude of the control signal towards the desired magnitude.

A load control device may be configured to control a load regulationdevice that is adapted to control the power delivered to an electricalload. The load control device may be configured to determine if a faultcondition exists at a control terminal that is adapted to be coupled tothe load regulation device. The load control device may be configured tomonitor the magnitude of a voltage at the control terminal to determineif the fault condition exists at the control terminal. For example, theload control device may monitor the magnitude of a voltage at thecontrol terminal to determine if the load regulation device iscompatible or incompatible with the communication circuit of the loadcontrol device. The load control device may be configured to determinethat the load regulation is compatible with the load control device, forexample, if the load regulation device is generating a link supplyvoltage at the control terminal. The load control device may beconfigured to determine that the load regulation device is incompatiblewith the communication circuit if the link supply voltage is not presentat the control terminal, below a predetermined threshold value, and/orthe like. If the load control device determines that the load regulationdevice is incompatible with the communication circuit, the load controldevice may determine that a fault condition exists at the controlterminal and operate in a fault mode. The load control device mayoperate as an electronic switch in the fault mode (e.g., as opposed to adimmer switch).

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an example wall-mountable load controldevice.

FIG. 2 is a simplified block diagram of an example 0-10V load controldevice.

FIG. 3 shows example plots of a magnitude of a control signal withrespect to a desired light intensity of a lighting load.

FIG. 4 is an example flowchart of a control procedure.

FIG. 5 is an example flowchart of a startup procedure.

DETAILED DESCRIPTION

Described herein are examples of a load control system for controllingthe amount of power delivered to an electrical load, such as a lightingload, and more particularly, to a wall-mounted load control device forcontrolling a load regulation device, such as a light-emitting diode(LED) driver for an LED light source, via a control signal, such as a0-10V control signal.

FIG. 1 is a perspective view of an example wall-mountable load controldevice 100. In an example, the wall mountable load control device 100may comprise a sensor dimmer switch. The load control device 100 may beadapted to be mounted in a single-gang electrical wallbox (not shown).The load control device 100 may comprise a plurality of electricalconnections (e.g., screw terminals or wires) adapted to be coupled to analternating-current (AC) power source (not shown) and an electricalload, for example, a lighting load (not shown). The load control device100 may be adapted to be coupled in series electrical connection betweenthe AC power source and the load for controlling the power delivered tothe load. For example, the electrical load may comprise a loadregulation circuit for driving a lighting load, such as an LED driverfor controlling an LED light source. The load control device 100 may beconfigured to generate a control signal (e.g., a 0-10V control signal)that is coupled to the LED driver via a control wiring for controllingthe intensity of the LED light source.

The load control device 100 may comprise a yoke (not shown) for mountingthe load control device 100 to the electrical wallbox. The load controldevice 100 may comprise a faceplate 102 that is mechanically coupled tothe yoke and has an opening 104 through which a bezel 106 of the loadcontrol device 100 may be received. The load control device 100 mayfurther comprise a toggle actuator 108 (e.g., a control button) and anintensity adjustment actuator 110 (e.g., a rocker switch) arranged onthe bezel 106. Successive actuations of the toggle actuator 108 maytoggle, i.e., turn off and on, the lighting load. Actuations of an upperportion 116 or a lower portion 118 of the intensity adjustment actuator110 may respectively increase or decrease the amount of power deliveredto the lighting load and thus increase or decrease the intensity of thelighting load from a minimum intensity (e.g., approximately 1%) to amaximum intensity (e.g., approximately 100%).

The load control device 100 may further comprise a lens 114 arranged onthe bezel 106. The load control device 100 may comprise an internaldetector. The load control device 100 may be configured to detectoccupancy and vacancy conditions in the space around (i.e., in thevicinity of) the load control device 100 using, for example, theinternal detector. The internal detector may comprise a pyroelectricinfrared (PIR) detector, which is operable to receive infrared energyfrom an occupant in the space via the lens 114 to thus sense theoccupancy or vacancy condition in the space. The internal detector maycomprise an ultrasonic detector, a microwave detector, or anycombination of PIR detectors, ultrasonic detectors, and/or microwavedetectors. The load control device 100 may be configured to turn on theelectrical load in response to detecting an occupancy condition in thespace and to turn off the electrical load in response to detecting avacancy condition in the space. An example of a load control deviceconfigured to control an electrical load in response to detectingoccupancy and vacancy conditions in described in greater detail incommonly-assigned U.S. Patent Application Publication No. 2012/0313535,published Dec. 13, 2012, entitled METHOD AND APPARATUS FOR ADJUSTING ANAMBIENT LIGHT THRESHOLD, the entire disclosure of which is herebyincorporated by reference.

The load control device 100 may further comprise a plurality of visualindicators 112, e.g., light-emitting diodes (LEDs), which may bearranged in a linear array on the bezel 106. The visual indicators 112may be illuminated to provide feedback of the intensity of the lightingload. The load control device may further comprise an LED 120 positionedto illuminate the lens 114 to provide feedback to the user (e.g., duringa programming mode and/or when the load control device detects anoccupancy and/or vacancy condition). Examples of wall-mounted dimmerswitches are described in greater detail in U.S. Pat. No. 5,248,919,issued Sep. 29, 1993, entitled LIGHTING CONTROL DEVICE, and U.S. patentapplication Ser. No. 13/780,514, filed Feb. 28, 2013, entitled WIRELESSLOAD CONTROL DEVICE, the entire disclosures of which are herebyincorporated by reference.

FIG. 2 is a simplified block diagram of an example of a 0-10V loadcontrol device 200. For example, the 0-10V load control device 200 maybe an example of the wall-mountable load control device 100 shown inFIG. 1 . The load control device 200 may comprise a hot terminal Hadapted to be coupled to an AC power source 202 and a switched hotterminal SH adapted to be coupled to an electrical load. For example,the electrical load may comprise a load regulation circuit for driving alighting load, such as an LED driver 204 for controlling an LED lightsource 206. The LED driver 204 may be configured to control the powerdelivered to the LED light source 206, and thus the intensity of the LEDlight source 206 in response to a direct-current (DC) control signalV_(CS) received from the load control device 200 via a control wiring208. The LED driver 204 may be configured to turn the LED light source206 on and off, and/or to adjust the intensity of the LED light source206 between a low-end (e.g., minimum) intensity L_(LE) and a high-end(e.g., maximum) intensity L_(HE). The LED driver 204 may be configuredto control the power delivered to the LED light source 206, for example,by regulating the voltage generated across the LED light source 206and/or regulating the current conducted through the LED light source206. Examples of an LED driver are described in greater detail incommonly-assigned U.S. Pat. No. 8,492,987, issued Jul. 23, 2013,entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE,and U.S. Patent Application Publication No. 2014/0009084, published Jan.9, 2014, entitled FORWARD CONVERTER HAVING A PRIMARY-SIDE CURRENT SENSECIRCUIT, the entire disclosures of which are hereby incorporated byreference. Alternatively, the electrical load may comprise an electronicballast for driving a fluorescent lamp.

The load control device 200 may comprise a control circuit 210. Thecontrol circuit 210 may control the operation of the load control device200. For example, the control circuit 210 may generate the controlsignal V_(CS) for adjusting the intensity of the LED light source 206.The control circuit 210 may comprise any suitable controller orprocessing device, such as, for example, a microprocessor, aprogrammable logic device (PLD), a microcontroller, or an applicationspecific integrated circuit (ASIC). The load control device 200 maycomprise a controllably conductive device 212 coupled in serieselectrical connection between the hot terminal H and the switched hotterminal SH for controlling the power delivered to the LED driver 204and the LED light source 206. The controllably conductive device 212 maycomprise a switching circuit, such as, for example, a relay, or abidirectional semiconductor switch, such as, for example, a triac, oneor more silicon-controlled rectifiers (SCRs), a field-effect transistor(FET) in a rectifier bridge, two FETs in anti-series connection, one ormore insulated-gate bipolar junction transistors (IGBTs), or anysuitable semiconductor switching circuit. The control circuit 210 may becoupled to the controllably conductive device 212 for rendering thecontrollably conductive device 212 conductive and non-conductive to thuscontrol the power delivered to the LED driver 204 and the LED lightsource 206 (e.g., to turn the LED light source 206 on and off, and/or toadjust the intensity of the LED light source 206 between the low-endintensity L_(LE) and the high-end intensity L_(HE)).

The control circuit 210 may be configured to receive inputs from one ormore control buttons 214 (e.g., the toggle actuator 108 and/or theintensity adjustment actuator 110 of the load control device 100 shownin FIG. 1 ). The control circuit 210 may be configured to render thecontrollably conductive device 212 conductive and non-conductive to turnthe LED light source 206 on and off in response to actuations of thecontrol buttons 214. The control circuit 210 may be configured tooperate in a dimmer mode in which the control circuit determines adesired light intensity L_(DE)s for the LED light source 206 in responseto actuations of the control buttons 214 and controls the control signalV_(CS) to adjust the intensity of the LED light source to the desiredlight intensity (e.g., between the low-end intensity L_(LE) and thehigh-end intensity L_(HE)).

When the control circuit 210 is operating in the dimmer mode and atoggle actuator (e.g., the toggle actuator 108) is actuated, the controlcircuit 210 may be configured to “fade” the LED light source 206 on andoff (e.g., to gradually adjust the intensity on and off over a fadeperiod). For example, when fading the LED light source 206 off, thecontrol circuit 210 may be configured to control the control signalV_(CS) to gradually adjust the intensity of the LED light source 206towards the low-end intensity L_(LE) over the fade period and thenrender the controllably conductive device 212 non-conductive at the endof the fade period to turn the LED light source off.

The load control device 200 may further comprise one or more visualindicators 216 (e.g., LEDs). The visual indicators 112 of the loadcontrol device 100 may be an example of the visual indicators 216. Thecontrol circuit 210 may be coupled to the visual indicators 216 toilluminate the visual indicators 216 to provide feedback to a user. Inaddition, one of the visual indicators 216 (e.g., the LED 120) may bepositioned to illuminate a lens (e.g., the lens 114) of the load controldevice 200.

The control circuit 210 may also be coupled to a memory 218, forexample, for storage of operational characteristics of the load controldevice 200. The memory 218 may be implemented as an external integratedcircuit (IC) or as an internal circuit of the control circuit 210. Thecontrol circuit 210 may be configured to modify the operationalcharacteristics stored in the memory in response to a user executing anadvanced programming mode of the load control device 200, e.g., inresponse to one or more actuations of the control buttons 214. Anexample of an advanced programming mode for a wall-mountable loadcontrol device is described in greater detail in U.S. Pat. No.7,190,125, issued Mar. 13, 2007, entitled PROGRAMMABLE WALLBOX DIMMER,the entire disclosure of which is hereby incorporated by reference.

The load control device 200 may further comprise a sensor circuit. Forexample, the sensor circuit may comprise an occupancy detection circuit220 operable to detect an occupancy or vacancy condition in the vicinityof the load control device 200. The occupancy detection circuit 220 maycomprise a detector for detecting an occupancy or vacancy condition inthe space. The detector may comprise one or more of a pyroelectricinfrared (PIR) detector, an ultrasonic detector, and/or a microwavedetector. For example, a PIR detector may be operable to receiveinfrared energy from an occupant in the space around the load controldevice 200 through a lens (e.g., the lens 114 shown in FIG. 1 ) to thussense the occupancy condition in the space. The control circuit 210 maybe configured to determine a vacancy condition in the space after atimeout period expires since the last occupancy condition was detected.The control circuit 210 may be configured to turn the LED light source206 on and off and to adjust the intensity of the LED light source 206in response to the occupancy detection circuit 220 detecting occupancyand/or vacancy conditions.

The load control device 200 may comprise a communication circuit, e.g.,a wireless communication circuit 222 for transmitting and/or receivingwireless signals. For example, the wireless communication circuit 222may comprise a radio-frequency (RF) transceiver, an RF receiver, an RFtransmitter, an infrared (IR) receiver, and/or other suitable wirelesscommunication circuit. The load control device 200 may be operable toreceive wireless signals from an input device, for example, a remotewireless occupancy or vacancy sensor, a networked device (e.g., a mobiledevice), a remote control device, and/or the like. The control circuit210 may be operable to control the LED light source 206 in response tothe wireless signals received from the input device. For example, thecontrol circuit 210 may be operable to control the LED light source 206in response to the wireless signals received from the remote wirelessoccupancy or vacancy sensor in a similar manner as the control circuitoperates in response to the internal occupancy detection circuit 220.Examples of remote wireless occupancy and vacancy sensors are describedin greater detail in commonly-assigned U.S. Pat. No. 7,940,167, issuedMay 10, 2011, entitled BATTERY-POWERED OCCUPANCY SENSOR; U.S. Pat. No.8,009,042, issued Aug. 11, 2011, entitled RADIO-FREQUENCY LIGHTINGCONTROL SYSTEM WITH OCCUPANCY SENSING; and U.S. Pat. No. 8,199,010,issued Jun. 12, 2012, entitled METHOD AND APPARATUS FOR CONFIGURING AWIRELESS SENSOR, the entire disclosures of which are hereby incorporatedby reference. The communication circuit 222 may comprise a wiredcommunication circuit operable to transmit and receive digital messagesover a wired communication link, such as, for example, a serialcommunication link, an Ethernet communication link, a power-line carriercommunication link, and/or other suitable digital communication link.

The load control device 200 may comprise a power supply 224 forgenerating a direct-current (DC) supply voltage V_(CC) for powering thecontrol circuit 210, the memory 218, the wireless communication circuit222, and/or other low-voltage circuitry of the load control device 200.The power supply 224 may be coupled between the hot terminal H and anearth ground terminal EGND that may be coupled to an earth groundconnection in the electrical wallbox in which the load control device200 is mounted. The load control device 200 may (e.g., alternatively)comprise a neutral connection (not shown) adapted to be coupled to theneutral side of the AC power source 202, and the power supply 224 couldbe coupled between the hot terminal H and the neutral terminal. The loadcontrol device 200 could comprise a “two-wire” device that does notrequire an electrical connection to earth ground or neutral, and has oneor more power supplies adapted to conduct a charging current through theLED driver 204.

The load control device 200 may comprise first and second controlterminals C1, C2 adapted to be coupled to the LED driver 204 via thecontrol wiring 208. The load control device 200 may comprise a drivercommunication circuit 230 (e.g., a 0-10V circuit) for generating acontrol signal V_(CS) (e.g., a 0-10V control signal or a 10-0V controlsignal). The driver communication circuit 230 may comprise a currentsink circuit 232 adapted to sink current through the LED driver 204 viathe control wiring 208. The current sink circuit 232 may becharacterized by linear or non-linear operation. The LED driver 204 maybe configured to generate a link supply voltage (e.g., approximately 10V) to allow the current sink circuit 232 to generate the control signalV_(CS) on the control wiring 208.

The control circuit 210 may generate a direct-current (DC) output signalV_(DC) and send the output signal V_(DC) to the communication drivercircuit 230. For example, the control circuit 210 may comprise adigital-to-analog converter (DAC) for generating a DC output signalV_(DC) that is received by the current sink circuit 232 for generatingthe control signal V_(CS). The control circuit 210 may adjust themagnitude of the control signal V_(CS) by adjusting the magnitude of theoutput signal V_(DC). The control circuit 210 may control the outputsignal V_(DC) in order to control the magnitude of the control signalsV_(CS) to have a desired DC magnitude V_(DES) For example, the controlcircuit 210 may control the magnitude of the control signals V_(CS) tohave a desired DC magnitude V_(DES) that ranges between zero and tenvolts and indicates a target intensity for the LED light source 206(e.g., indicates a target amount of power to be delivered to the LEDlight source 206). Alternatively, the output signal V_(DC) couldcomprise a pulse-width modulated (PWM) signal or variable-frequencywaveform, in response to which the current sink circuit 232 isconfigured to adjust the magnitude of the control signal V_(CS). Inaddition, the driver communication circuit 230 could (e.g.,alternatively) comprise a current source circuit or a currentsource/sink circuit for generating the control signal V_(CS) in responseto the output signal V_(DC).

The control circuit 210 may be configured to receive the feedback signalindicating the magnitude of the control signal V_(CS) generated by thecurrent sink circuit 232. For example, the driver communication circuit230 may comprise a scaling circuit 234 (e.g., a resistor divider) forgenerating a feedback voltage V_(FB), which may be a scaled version ofthe control signal V_(CS). The control circuit 210 may receive (e.g.,sample) the feedback voltage V_(FB). The control circuit 210 maydetermine a difference between the magnitude of the control signalV_(CS) and the desired DC magnitude V_(DES). The control circuit mayadjust the magnitude of the output signal V_(DC) in response to thedifference between the magnitude of the control signal V_(CS) and thedesired DC magnitude V_(DES), for example, so as to adjust the magnitudeof the control signal V_(CS) towards the desired DC magnitude V_(DES).

FIG. 3 shows example plots of the magnitude of the control signal V_(CS)with respect to the desired light intensity of the LED light source 206(e.g., as determined from the user inputs provided by the controlbuttons 214 and/or the output signal V_(DC)) The control circuit 210 mayadjust the DC magnitude of the control signal V_(CS) to indicate thetarget intensity of the LED light source 206 to the LED driver 204 inone of a plurality of dimming modes, e.g., a linear mode and/or asquare-law mode. For example, in the linear mode, the desired magnitudeV_(DES) of the control signal V_(CS) may be a linear function of thedesired light intensity L_(DES) of the LED light source 206, forexample, as shown by a linear plot 300 in FIG. 3 . In the square-lawmode, the desired magnitude V_(DES) of the control signal V_(CS) may bea non-linear function of the desired light intensity L_(DES) of the LEDlight source 206 (e.g., a predetermined relationship), for example, asshown by a square-law plot 302 in FIG. 3 . A square-law mode may providefor the actual light output of the LED light source 206 to be perceivedto be linear by the human eye with respect to the desired lightintensity L_(DES) indicated by the control buttons 214. The controlcircuit 210 may be configured to switch between the linear mode and thesquare-law mode, for example, in response to inputs received during theadvanced programming mode of the load control device 200.

The control circuit 210 may control the control signal V_(CS) to beeither a 0-10V control signal or a 10-0V control signal. When receivinga 0-10V control signal, the LED driver 204 may control the LED lightsource 206 to the low-end intensity L_(LE) when the 0-10V control signalhas a magnitude of zero volts, to the high-end intensity L_(HE) when the0-10V control signal has a magnitude of ten volts, and to an intensitythat is scaled (e.g., linearly or non-linearly depending on the dimmingmode) between the low-end intensity L_(LE) and the high-end intensityL_(HE) when the 0-10V control signal has a magnitude between zero andten volts. When receiving a 10-0V control signal, the LED driver 204 maycontrol the LED light source 206 to the low-end intensity L_(LE) whenthe 10-0V control signal has a magnitude of ten volts, to the high-endintensity L_(HE) when the 10-0V control signal has a magnitude of zerovolts, and to an intensity that is scaled (e.g., linearly ornon-linearly depending on the dimming mode) between the low-endintensity L_(LE) and the high-end intensity L_(HE) when the 10-0Vcontrol signal has a magnitude between ten and zero volts.

The actual magnitude of the control signal V_(CS) may not correspondwith the desired magnitude V_(DES) as intended by the control circuit210, for example, due to non-linear operation of the current sinkcircuit 232 and/or the hardware of the LED driver 204 to which thecontrol terminals C1, C2 are connected. When the control circuit 210 isoperating in a linear mode (e.g., according to the linear plot 300) or anon-linear mode (e.g., according to the square law plot 302), the actualmagnitude of the control signal V_(CS) may not correspond with thedesired plot (e.g., linear plot 300 or square law plot 302). Forexample, the actual magnitude of the control signal V_(CS) maycorrespond with an unintended plot, such as plots 304, 306, or 308 inFIG. 3 . The control circuit 210 may be configured to monitor themagnitude of the control signal V_(CS) and to adjust the magnitude ofthe output signal V_(DC) to compensate for errors in the magnitude ofthe control signal V_(CS) (e.g., using closed loop control). Forexample, the control circuit 210 may sample the feedback signal V_(FB)from the scaling circuit 234 to determine the magnitude of the controlsignal V_(CS). If the magnitude of the control signal V_(CS) is equal(e.g., approximately equal) to the desired magnitude V_(DES), thecontrol circuit 210 may not adjust the magnitude of the output signalV_(DC). However, if the magnitude of the control signal V_(CS) isdifferent than the desired magnitude V_(DES), the control circuit 210may calculate an error e_(CS) between the magnitude of the controlsignal V_(CS) and the desired magnitude V_(DES) (e.g.,e_(CS)=V_(CS)−V_(DES)), and determine a control signal adjustment valueΔ_(CS) based upon the calculated error e_(CS). The control circuit 210may then adjust the magnitude of the output signal V_(DC) using thecontrol signal adjustment value Δ_(CS) (e.g., V_(DC)=V_(DC)+Δ_(CS)) tobring the magnitude of the control signal V_(CS) towards the desiredmagnitude V_(DES) (e.g., to the magnitudes shown by linear plot 300 orthe square-law plot 302 in FIG. 3 ). For example, the control circuit210 may use closed loop integral control to adjust the magnitude of theoutput signal V_(DC) in response to the error e_(CS).

When the control circuit 210 turns the LED light source 206 on, theremay be a delay between the time at which the controllably conductivedevice 212 is rendered conductive and the time at which the LED driver204 is powered up and generating the link supply voltage. Because ofthis delay, the error e_(CS) between the magnitude of the control signalV_(CS) and the desired magnitude may have a large value before the LEDdriver 204 begins generating the link supply voltage. Accordingly, whenturning on and/or off the LED light source 206, the control circuit 210may override the closed loop control of the output signal V_(DC) Forexample, when turning on the LED light source 206, the control circuit210 may not adjust the magnitude of the output signal V_(DC) in responseto the error e_(CS) and may feed a predetermined value into DAC for atime period after the controllably conductive device 212 is renderedconductive. The predetermined value may be, for example, a low-endDAC-input value that corresponds to the low-end intensity L_(LE). Thismay be performed to ensure that the LED driver 204 has time to begingenerating the link supply voltage before the control circuit 210 usesclosed loop control to adjust the magnitude of the output signal V_(DC),and/or, for example, may avoid instability and oscillations in themagnitude of the control signal V_(CS) when the control circuit 210 isturning on the LED light source 206. The control circuit 210 mayoverride the closed loop control of the output signal V_(DC) whenturning off the LED light source 206, for example, and fade the LEDlight source 206 to off according to a predetermined fade rate.

The control circuit 210 may be configured to measure and store thelow-end DAC-input value that may be used when overriding the closed loopcontrol. For example, the control circuit 210 may be configured tomeasure the value that is input to the DAC when the control circuit 210is fading the LED light source off and the intensity of the LED lightsource is at the low-end intensity L_(LE). The control circuit 210 maybe configured to store this measured value in the memory 218 as thelow-end DAC-input value.

The control circuit 210 may also be configured to monitor the magnitudeof the voltage at the first control terminal C1 (e.g., the controlsignal V_(CS)) to determine if a fault condition exists. A faultcondition may exist due to a miswire condition on the control wiring 208coupled to the control terminals C1, C2. For example, a miswirecondition may exist if the control terminals C1, C2 are shortedtogether, if at least one of the control terminals C1, C2 is not coupledto the control wiring 208, and/or if the control wiring 208 is notcoupled to an LED driver. In addition, a fault condition may exist whenthe LED driver 204 that requires the load control device 200 to sourcecurrent via the control terminals C1, C2 is coupled to the load controldevice 200. As shown in FIG. 2 , the driver communication circuit 230 ofthe load control device 200 may comprise the current sink circuit 232(e.g., and not a current source circuit). Accordingly, the load controldevice 200 may not be configured to control an LED driver that requiresthe load control device 200 to source current via the control terminalsC1, C2. An LED driver that requires the load control device 200 tosource current will not generate the link supply voltage on the controlwiring 208. Accordingly, before beginning to generate the output signalV_(DC) to thus generate the control signal V_(CS) on the control wiring208 (e.g., a startup), the control circuit 210 may be configured tomonitor the magnitude of the voltage at the first control terminal C1 todetermine if the connected LED driver 204 is generating the link supplyvoltage or not. If the link supply voltage is present on the controlwiring 208, the control circuit 210 may then operate in a normal mode togenerate the control signal V_(CS) to control the LED driver 204.

However, if the control circuit 210 determines that a fault conditionexists, the control circuit 210 may enter a fault mode (e.g., as opposedto the normal mode of operation). For example, if the link supplyvoltage is not present on the control wiring 208, the control circuit210 may enter a fault mode. In the fault mode, the control circuit 210may blink one or more of the visual indicators 216 and/or illuminate thelens (e.g., the lens 114) to indicate to a user that a miswire conditionmay exist or an incompatible LED driver may be coupled to the loadcontrol device 200. For example, the control circuit 210 may blink oneor more of the visual indicators 216 and/or illuminate the lens when theload control device 200 is powered up and the control circuit 210determines that the link supply voltage is not present on the controlwiring 208. In addition, the control circuit 210 may blink one or moreof the visual indicators 216 and/or illuminate the lens when the controlcircuit 210 is operating in the fault mode and the intensity adjustmentactuator 110 is actuated (e.g., a user is trying to adjust the intensityof the controlled LED light source).

In the fault mode, the load control device 200 may not be able to adjustthe intensity of the LED light source 206 (e.g., due to the miswirecondition on the load wiring or an incompatible LED driver coupled tothe load control device 200). For example, if the control circuit 210attempts to fade the LED light source off in the fault mode, theintensity of the LED light source 206 may stay at the maximum intensitywhile the control circuit is controlling the control signal V_(CS) togradually decrease the intensity, and then turn off the LED light sourceafter the fade period when the controllably conductive device 212 isrendered non-conductive. This condition may appear to a user as a delayin turning off the LED light source (e.g., rather than fading to off).

Accordingly, when the control circuit 210 is in the fault mode, thecontrol circuit 210 may be configured to operate in a switch mode inwhich the load control device 200 operates as if the load control device200 were an electronic switch (e.g., rather than operating as a dimmerswitch in the dimmer mode). In the switch mode, the control circuit 210may only be able to control the controllably conductive device 212 toturn the LED light source 206 on and off in response to actuations ofthe toggle actuator 108. For example, in the switch mode, the controlcircuit 210 may simply switch the setpoint for the LED light sourcebetween 100% (e.g., when the LED light source is on) and 0% (e.g., whenthe LED light source is off). The control circuit 210 may be configuredto control the fade period to zero seconds when in the switch mode, suchthat the control circuit 210 controls the controllably conductive device212 to immediately turn on and off the LED light source in response toactuations of the toggle actuator 108.

The control circuit 210 may be configured to monitor the magnitude ofthe voltage at the first control terminal C1 to determine if a faultcondition exists whenever the unit is powered up. For example, thecontrol circuit 210 be configured to wait for a delay period (e.g.,approximately five seconds) before determining if a fault conditionexits on the control wiring 208 (e.g., to allow the LED driver 204 topower up and begin generating the link supply voltage). In addition,when operating in the fault mode, the control circuit 210 may monitor(e.g., periodically monitor) the magnitude of the voltage at the firstcontrol terminal C1 (e.g., the control signal V_(CS)) to determine ifthe fault condition has ceased. For example, the control circuit 210 mayswitch from the fault mode to the normal mode if the LED driver 204 actslike a source (e.g., the LED driver 204 is stable). The control circuit210 may be configured to switch back to the normal mode in response todetermining that the link supply voltage is present on the controlwiring 208. For example, the control circuit 210 may be configured tochange back to the normal mode if the magnitude of the voltage V_(CS) atthe control terminal is greater than a predetermined voltage threshold(e.g., approximately 1000 mV).

The control circuit 210 could be configured to monitor the magnitude ofthe voltage at the first control terminal C1 to determine how toappropriately generate the control signal V_(CS). For example, thedriver communication circuit 230 of the load control device 200 maycomprise a current source/sink circuit (e.g., in lieu of the currentsink circuit 232). The current source/sink circuit may operate as eithera current source or a current sink. If the driver communication circuit230 comprises a current source/sink circuit, the control circuit 210 maydetermine whether the current source/sink circuit should source or sinkcurrent depending whether the link supply voltage is present at thefirst control terminal C1 or not. For example, if the link supplyvoltage is present on the control wiring 208, the control circuit 210could control the current source/sink circuit to sink current, and ifthe link supply voltage is not present on the control wiring, thecontrol circuit could control the current source/sink circuit to sourcecurrent.

The load control device 200 may comprise a photodetector 240. Thephotodetector 240 may comprise a reverse-biased LED, an opticaldetector, a photoresistor, a photovoltaic cell, an active-pixel sensor,and/or the like. The photodetector 240 may be integral to the loadcontrol device 200 or remote from the load control device 200. Forexample, the photodetector 240 may be located inside of the load controldevice 200 adjacent to the occupancy detection circuit 220. Thephotodetector 240 may receive ambient light outside of the load controldevice 200 through a lens (e.g., the lens 114). The load control device200 may receive information from the photodetector 240 indicating anambient light level in the vicinity of the load control device 200.

The load control device 200 (e.g., the control circuit 210) may use thephotodetector 240 to determine whether or not to turn on the LED lightsource 206 in response to an occupancy condition. For example, the loadcontrol device 200 may receive an occupancy condition from thephotodetector 240, measure the ambient lighting level (e.g., with theLED light source 206 off) using the photodetector 240, and compare theambient lighting level against a threshold. If the ambient lightinglevel is below the threshold (e.g., there is not sufficient light in thespace for a user to see), the load control device 200 may turn on theLED light source 206. If the ambient lighting level is above thethreshold (e.g., there is sufficient light in the space), the loadcontrol device 200 may not turn on the LED light source 206, forexample, to increase energy savings. The load control device 200 maythen be configured to turn on the LED light source 206 in response toactuations of the control buttons 214.

The load control device 200 (e.g., the control circuit 210) may use thephotodetector 240 to perform daylighting. For example, the load controldevice 200 may determine the ambient lighting level using thephotodetector 240, and adjust the output signal V_(DC) to compensate forthe ambient light level in the space, for example, to increase energysavings.

The load control device 200 (e.g., the control circuit 210) maydetermine a dimming mode (e.g., a dim curve model) of the LED driver 204and LED light source 206, for example, using the photodetector 240. Forexample, the load control device 200 may be placed in the advancedprogramming mode. The ambient light may be determined, for example,using the photodetector 240 when the LED light source 206 is off. Theload control device 200 (e.g., the control circuit 210) may adjust theoutput signal V_(DC) such that the desired intensity of the LED lightsource 206 is adjusted through a plurality of different intensitylevels, for example, 0% (i.e., off), 25%, 50%, 75%, and 100%. Whileadjusting the intensity of the output signal V_(DC), the photodetector240 may measure the intensity level of the LED light source 206. Theload control device 200 may remove the ambient light, as measured by thephotodetector 240, from intensity levels of the LED light source 206. Ifthe procedure is executed at night (e.g., when the ambient light levelis below a predetermined threshold), the load control device 200 may notneed to remove the ambient light from the intensity levels of the LEDlight source 206. The load control device 200 may also receive feedbackfrom a daylight sensor, and use the daylight information to furtherrefine the measured intensity level of the LED light source 206 at theplurality of different intensity levels. The load control device 200 maycorrelate the values of the output signal V_(DC) with the measuredintensity levels of the LED light source 206 to determine the dimmingmode of and/or for the LED driver 204 and LED light source 206. Forexample, the load control device 200 may determine which of a pluralityof predefined dimming modes most closely matches the results todetermine the dimming mode of and/or for the LED driver 204 and LEDlight source 206. The load control device may calibrate a dimming modethat is unique for the LED driver 204 and LED light source 206. Forexample, the load control device 200 may determine a piecewiselinearization table to generate a unique dimming mode for the LED driver204 and LED light source 206 (e.g., calculate each point based on theplurality of different intensity levels, calculate the slope betweeneach point, and use the points and slope to compute the valuesin-between). The load control device 200 may be configured to switchbetween one or more dimming modes, for example, when placed in theadvanced programming mode.

The load control device 200 (e.g., the control circuit 210) may use thephotodetector 240 to measure/detect flickering of the LED light source206. For example, if the control circuit 210 determines that the LEDlight source 206 is flickering and the LED light source 206 is beingoperated at or near the low-end intensity L_(LE), then the controlcircuit 210 may increase (e.g., trim) the low-end intensity L_(LE) levelof the LED light source 206, for example, to prevent flickering of theLED light source 206 at low-end.

FIG. 4 is a flowchart of an example control procedure 400 executed by acontrol circuit of a load control device (e.g., the control circuit 210of the load control device 200 shown in FIG. 2 ). The control circuitmay execute the control procedure 400 in order to generate a DC outputsignal (e.g., the output signal V_(DC)) for causing a communicationcircuit (e.g., the driver communication circuit 230) to generate acontrol signal (e.g., the control signal V_(CS)) for controlling a loadregulation device (e.g., LED driver 204) for an electrical load (e.g.,the LED light source 206). The control circuit may execute the controlprocedure 400 executed periodically (e.g., every 25 ms). The controlprocedure 400 may start at 410. At 412, the control circuit may receive(e.g., sample) a feedback signal that indicates the magnitude of thecontrol signal V_(CS) (e.g., the feedback signal V_(FB)). The controlcircuit may determine the magnitude of the control signal V_(CS) at 414,e.g., by scaling the sampled magnitude of the feedback signal V_(FB) bya constant k (e.g., approximately four). If the magnitude of the controlsignal V_(CS) is equal (e.g., approximately equal) to the desiredmagnitude V_(DES) at 416, the control procedure 400 may simply exit thecontrol procedure 400 without adjusting the output signal V_(DC).

However, if the magnitude of the control signal V_(CS) is not equal(e.g., approximately equal) to the desired magnitude V_(DES) at 416, thecontrol circuit may calculate the difference between the magnitude ofthe control signal V_(CS) and the desired magnitude V_(DES) to determinean error e_(CS) at 418 (e.g., e_(CS)=V_(CS)−V_(DES)). The controlcircuit may then determine a control signal adjustment value Δ_(CS)using the error e_(CS) at 420, e.g., by calculating the control signaladjustment value Δ_(CS) as a function of the error e_(CS). The controlcircuit may then adjust the magnitude of the output signal V_(DC) toadjust the magnitude of the control signal V_(CS) towards the desiredmagnitude V_(DES) at 422, e.g., by applying the control signaladjustment value Δ_(CS) to the output signal V_(DC), before the controlprocedure 400 exits.

FIG. 5 is a flowchart of an example startup procedure 500 by a controlcircuit of a load control device (e.g., the control circuit 210 of theload control device 200 shown in FIG. 2 ). The control circuit mayexecute the startup procedure 500 in order to initialize a communicationcircuit (e.g., the driver communication circuit 230) for generating acontrol signal (e.g., the control signal V_(CS)) for controlling a loadregulation device (e.g., the LED driver 204) for an electrical load(e.g., the LED light source 206). For example, the control circuit mayexecute the startup procedure 500 to determine if the load regulationdevice is compatible with the communication circuit of the load controldevice. The control circuit may execute the startup procedure 500 atstartup of the control circuit at 510, e.g., when the load controldevice 200 is first powered up. At 512, the control circuit may render acontrollably conductive device (e.g., the controllably conductive device210) conductive to apply power to the load regulation device. At 514,the control circuit may receive (e.g., sample) a feedback signal thatindicates the magnitude of a voltage V_(CS) at a control terminalcoupled to the load regulation device (e.g., the feedback signalV_(FB)). The control circuit may wait (e.g., for approximately fiveseconds) before sampling the feedback signal that indicates themagnitude of a voltage V_(CS) at a control terminal coupled to the loadregulation device (e.g., the feedback signal V_(FB)) at 514. The controlcircuit may determine the magnitude of the voltage V_(CS) at the controlterminal at 516, e.g., by scaling the sampled magnitude of the feedbacksignal V_(FB) by a constant k (e.g., approximately four).

If the magnitude of the voltage V_(CS) at the control terminal isgreater than a first predetermined threshold V_(TH1) (e.g.,approximately 300 mV) at 518 (e.g., if the link supply voltage ispresent at the control terminal), the control circuit may enter a normalmode at 520 and the startup procedure 500 exits. During the normal mode,the control circuit may control the magnitude of a control signal at thecontrol terminal to adjust the amount of power delivered to theelectrical load (e.g., normal operation of the load control device). Ifthe magnitude of the voltage V_(CS) at the control terminal is notgreater than the first predetermined threshold V_(TH1) at 518 (e.g., ifthe link supply voltage is not present at the control terminal), thecontrol circuit may render the controllably conductive devicenon-conductive at 522 to disconnect power from the load regulationdevice, and/or may enter a fault mode at 524, before the startupprocedure 500 exits. In the fault mode, the control circuit may blinkone or more of the visual indicators (e.g., the visual indicators 112,216) and/or illuminate a lens (e.g., the lens 114) to indicate to a userthat the load regulation device is incompatible with the load controldevice. The control circuit may change to a switch mode at 524. Thecontrol circuit may control the electrical load as an electronic switchin the switch mode as described above. When operating in the fault mode,the control circuit may be configured to change back to the normal mode,for example, if the magnitude of the voltage V_(CS) at the controlterminal is greater than a second predetermined threshold V_(TH2) (e.g.,approximately 1000 mV).

The invention claimed is:
 1. A load control device for controlling aload regulation device adapted to control power delivered from an ACpower source to a light fixture, the load control device comprising: acontrol circuit configured to generate an output signal for controllinga magnitude of a control signal to a desired magnitude, the desiredmagnitude indicating a target amount of power to be delivered to thelight fixture; a communication circuit coupled to the control circuit,the communication circuit including current sink circuit to receive alink supply voltage, sink current through a load regulation device, andgenerate a control signal; and a photodetector configured to detect alight level in the vicinity of the light fixture operatively coupled tothe load control device; wherein the control circuit is furtherconfigured to: place the light fixture in an OFF state; receive, fromthe photodetector, a value corresponding to a measured ambient lightlevel in the vicinity of the light fixture; adjust the magnitude of theoutput signal through each of a plurality of values; determine a valuecorresponding to the detected light level produced by the light fixtureat each of the plurality of values of the output signal using thephotodetector; correct the value corresponding to the detected lightlevel by subtracting the value corresponding to the measured ambientlight level; and correlate the corrected light levels and the pluralityof values of the output signal to determine a dimming curve model forthe load regulation device and light fixture.
 2. The load control deviceof claim 1, the control circuit to further: determine the dimming curvemodel by selecting between a plurality of preconfigured dimming curvemodels or by creating a dimming curve model using the correlation of theintensity levels of the light produced by the light fixture and theplurality of values of the output signal.
 3. The load control device ofclaim 2, wherein to determine the dimming curve model, the controlcircuit to further: receive daylight sensor feedback from a daylightsensor; subtract the daylight sensor feedback from the intensity levelof the light produced by the light fixture at each of the plurality ofvalues of the output signal to determine a refined intensity levelproduced by the light fixture at each of the plurality of values of theoutput signal; and correlate the refined intensity levels produced bythe light fixture and the plurality of values of the output signal todetermine the dimming curve model for the load regulation device and thelight fixture.
 4. The load control device of claim 1, the controlcircuit to further: detect flickering of the light fixture using thephotodetector; and responsive to the detection of flickering of thelight fixture, increase the output signal.
 5. A load control method tocontrol a load regulation device adapted to control power delivered froman AC power source to a light fixture, the method comprising:generating, by a control circuit, an output signal for controlling amagnitude of a control signal to a desired magnitude, the desiredmagnitude indicating a target amount of power to be delivered to thelight fixture; placing, by the control circuit, the light fixture in anOFF state; receiving, by the control circuit from the photodetector, avalue corresponding to a measured ambient light level in the vicinity ofthe light fixture; adjusting, by the control circuit, the magnitude ofthe output signal through each of a plurality of discrete values;generating, via a current sink circuit communicatively coupled to thecontrol circuit, a control signal using a link supply voltage;determining, by the control circuit via a communicatively coupledphotodetector circuit, a value corresponding to the detected light levelproduced by the light fixture at each of the plurality of values of theoutput signal; correcting, by the control circuit, the valuecorresponding to the detected light level by subtracting the valuecorresponding to the measured ambient light level; and correlating, bythe control circuit, the corrected light levels and the plurality ofvalues of the output signal to determine a dimming curve model for theload regulation device and lighting fixture.
 6. The load control deviceof method of claim 5, further comprising: determining, by the controlcircuit, the dimming curve model by selecting between a plurality ofpreconfigured dimming curve models or by creating a dimming curve modelusing the correlation of the intensity levels of the light fixture andthe plurality of values of the output signal.
 7. The load control methodof claim 6, wherein determining the dimming curve model furthercomprises: receiving, by the control circuit from a communicativelycoupled daylight sensor, a daylight sensor output signal; subtracting,by the control circuit, the daylight sensor output signal from theintensity level produced by the light fixture at each of the pluralityof values of the output signal; determining, by the control circuit, arefined intensity level produced by the light fixture at each of theplurality of values of the output signal; and correlating, by thecontrol circuit, the refined intensity levels produced by the lightfixture and the plurality of values of the output signal to determinethe dimming curve model for the load regulation device and lightfixture.
 8. The load control method of claim 5, further comprising:detecting, by the control circuit via the photodetector circuit,flickering of the light produced by the light fixture; and responsive tothe detection of flickering of the light produced by the lightingfixture, increasing, by the control circuit, the output signal.
 9. Anon-transitory, machine-readable, storage device that includesinstructions that, when executed by a control circuit coupled to a loadregulation device adapted to control power delivered from an AC powersource to a lighting fixture, cause the control circuit to: generate anoutput signal for controlling a magnitude of a control signal to adesired magnitude, the desired magnitude indicating a target amount ofpower to be delivered to the lighting fixture; place the light fixturein an OFF state; receive, via the photodetector circuit, a valuecorresponding to a measured ambient light level in the vicinity of thelight fixture; adjust the magnitude of the output signal through each ofa plurality of discrete values; cause a current sink circuit receiving alink supply voltage and communicatively coupled to the control circuitto generate a control signal based on the output signal; determine, viaa communicatively coupled photodetector circuit, a value correspondingto the detected light level produced by the lighting fixture at each ofthe plurality of values of the output signal; correct the valuecorresponding to the detected light level by subtracting the valuecorresponding to the measured ambient light level; and correlate thecorrected light levels and the plurality of values of the output signalto determine a dimming curve model for the load regulation device andlighting fixture.
 10. The non-transitory, machine-readable, storagedevice of claim 9 wherein the instructions, when executed by the controlcircuit, cause the control circuit to: determine the dimming curve modelby selecting between a plurality of preconfigured dimming curve modelsor by creating a dimming curve model using the correlation of theintensity levels of the electrical load and the plurality of values ofthe output signal.
 11. The non-transitory, machine-readable, storagedevice of claim 10, wherein the instructions that cause the controlcircuit to determine the dimming curve model further cause the controlcircuit to: receive, from a communicatively coupled daylight sensor, adaylight sensor output signal; subtract the daylight sensor outputsignal from the intensity level at each of the plurality of values ofthe output signal; determine a refined intensity level of the electricalload at each of the plurality of values of the output signal; andcorrelate the refined intensity levels of the electrical load and theplurality of values of the output signal to determine the dimming curvemodel for the load regulation device and electrical load.
 12. Thenon-transitory, machine-readable, storage device of claim 9 wherein theinstructions, when executed by the control circuit, cause the controlcircuit to: detect, via the photodetector circuit, flickering of theelectrical load; and responsive to the detection of flickering of thelighting fixture, increase the output signal.